Removal of Lead (II) and Cadmium (II) Ions from Wastewater Using Activated Carbon Derived from Macadamia Intergrifolia Nutshell Powder

Abstract

Industrialization in developing countries has led to the release of toxic pollutants which has become a health challenge. Major sources of water contamination by toxic pollutants includes pharmaceuticals, residues from agrochemicals, dyes and heavy metals. Lead and Cadmium are heavy metals of great concern due to their high levels of toxicity even in minute concentrations. Convectional methods for the removal of heavy metal ions from aqueous solution are expensive. Adsorption using low cost activated carbon is a cheap and effective technique which removes heavy metal ions from water. In this study removal of Pb (II) ions and Cd (II) ions using activated carbon derived from Macadamia intergrifolia nutshell powder are reported. Macadamia intergrifolia nutshells were purchased for Kenya nut company in Kiambu county. Activated carbon was made by soaking two kilograms of Macadamia intergrifolia nutshell powder in 50 % phosphoric acid for 24 hours, which was then oven dried for 48 hours at 105°C. Dried sample was charred using a heating mantle at 300°C followed by iginition in an electrical muffle furnace at 550°C for 30 minutes. After cooling, the sample was washed with 0.1 HCl to remove ash content, and then washed with 0.1M NaOH to neutralize pH. Optimization parameters such as pH, sorbent mass, contact time and initial metal ion concentration were studied. The level of the two heavy metal ions before and after adsorption was determined using flame atomic absorption spectrophotometer . Adsorption of Pb (II) ions and Cd (II) ions were found to increase with increase in pH until the optimum pH of 4 and 5 for Pb (II) ions and Cd (II) ions respectively. Furthermore, adsorption of both metal ions was found to increase with increase in sorbent mass until the optimum sorbent mass of 0.4 and 0.3 grams for Pb(II) ions and Cd (II) ions respectively.The adsorption increased with increase in contact time. The optimum contact time for Pb (II) ions and Cd (II) ions were found to be 60 and 75 minutes respectively. Adsorption isotherm for both metal ions were found to fit well in the Langmuir model where maximum adsorption capacity was found to be 4.093 and 7.818 mg/g for Pb (II) ions and Cd (II) ions respectively. According to the Langmuir model values of 1/n for Pb (II) ions and Cd (II) ions were 0.627 and 0.598 respectively. This indicated a favorable reaction. Kinetics studies were found to fit well in the pseudo second order model where the value of equilibrium adsorption capacity was found to be 2.521 and 2.500 mg/g for Pb (II) and Cd (II) respectively. FT-IR of activated carbon analysis showed that the presence of OH at Ѵmax 3389 cm-1, COO- at Ѵmax 2367 cm-1 , C=O at Ѵmax 1593 cm-1 and POOH at Ѵmax 1206 cm-1 . These functional groups may have been responsible for Pb(II) and Cd(II) ions adsorption onto activated carbon. Investigation on SEM on external morphology revealed that the surface of the activated carbon adsorbent had deep cavities and also irregular structures, which provided the binding sites for the attachment of Pb(II) ions and Cd(II) ions. The study showed that activated carbon derived from Macadamia intergrifolia nutshell powder has a good potential for use in the removal in Pb (II) and Cd (II) ions from wastewater.